U.S. regulators inadvertently raise a question about who's to blame for investor losses.

In a ruling last week, an administrative trial judge at the U.S. Securities and Exchange Commission suspended the Chinese branches of the Big Four accounting firms from practicing at the SEC for six months. As a consequence, these accountants will not be able to sign off on the books of Chinese companies listed in the U.S., which could force the Chinese firms to delist at least temporarily for lack of audited accounts. The Big Four are appealing the ruling.